Compressor unloader



July 11, 1939. E. R. WOLFERT COMPRESSOR UNLOADER Filed July 28, 1937INVENTOR mmm'a W.WOLF'ERT FROM EVAVORHTOR CONDENSER MPRESSOR PatentedJuly 11, 193 9 PATENT OFFICE COMPRESSOR UNLOADER Edward R. Wolfert,Springfield, Mass, assignor to Westinghouse Electric 81: ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationJuly 28, 1937, Serial No. 156,119

13 Claims.

My invention relates to refrigerating apparatus of the compression typeand particularly to means for unloading the compressor used with suchapparatus.

In refrigerating apparatus of the compression type, the refrigerantcompressed in the compressor is discharged at high pressure to acondenser and withdrawn as a vapor at low pressure from an evaporator.The compressor operates intermittently tmprovide the requiredrefrigeration and it is necessary for the satisfactory operation of thecompressor with a motor of minimum size, to reduce the starting load onthe compressor in some way until the motor driving the compressor hasbeen brought up to normal operating speed.

Heretofore, one way of reducing the starting load on a compressor hasbeen to equalize the pressures on the high and low sides of therefrigerating system when the compressor is shut down.

The objection to this method, when the crankcase is connected to the lowside and a refrigerant miscible in oil is used, is that the oil absorbsa greatly increased quantity of refrigerant at the higher pressureobtaining in the low side at such time. The absorption of refrigerant tosuch extent greatly increases the amount of slugging of the compressorvalves upon starting.

Another method of reducing the starting load in connection withcompressors of small capacity has been to equalize the pressures at themoment of starting. With larger compressors, however; the equalizationis not effected rapidly enough to reduce the starting current of themotor.

In accordance with my invention, the starting load on the compressor isreduced when the com-= pressor stops by partially equalizing thepressures on the high and low sides of the system. The extent to whichequalization of the pressures takes place is preferably controlled bythe pressure-- diflerential between the high and low sides and is suchthat a pressure low enough to avoid exeessive absorption of refrigerantby the lubricating oil is maintained in the low side of the systemduring the off cycle of the compressor. Thus starting of the compressoris facilitated and sing ging of the compressor valves is substantiallyreduced.

It is, therefore, an object of my invention to provide improved meansfor reducing the starting load on a compressor used with refrigeratingapparatus of the compression type.

It is another object of my invention to reduce the starting load on acompressor in order that a motor of minimum size may be used to drivethe compressor.

It is a further object of my invention to reduce the starting loadbefore the compressor starts without excessive absorption of refrigerantby the lubricating oil.

It is still another object of my invention to reduce the starting loadon a compressor in such a manner thatthe amount of refrigerant absorbedby the oil in the crankcase of the compressor will be held to'a minimum.

It is a still further object of my invention to prevent slugging of thecompressor valves upon starting the compressor by reducing to a minimumthe amount of refrigerant absorbed by the oil in the crankcase of thecompressor whfle the compressor is unloaded.

These and other objects are efiecte'd by my invention as will beapparent from the following description and claims taken in connectionwith the accompanying drawings, forming a part of this application, inwhich:

Fig. 1 shows diagrammatically a refrigerating system embodying one formof my invention; and,

Fig. 2 shows diagrammatically a second form of my invention which may beused with a refrig crating system similar to that shown in Fig. 1.

' Referring to Fig. 1 of the drawing for a detailed description of oneembodiment of my invention, I show a refrigerating system of thecompression type in which refrigerant vapor is compressed in acompressor it and is discharged therefrom at a relatively high pressurethrough a conduit M to a condenser it. The compressed refrigerant iscooled and condensed in the condenser l2 and flows as a liquid to anevaporator it through a conduit it and an expansion device shown,diagrammatically, at it. The evaporator it is lo cated within theenclosure to be cooled and the refrigerant evaporating in the evaporatorI3 passes as a vapor through a conduit ii to the suction side of thecompressor ll), completing the cycle. ii. reservoir of oil (not shown)is maintained in. the crankcase it, which is connected to the lowrside,for lubricating the working elements of the compressor iii. A motor 19provides the motive power for the compressor It and operatesintermittently in response to the temperature of the enclosure to becooled. The motor i9 is connected to a suitable source of energy througha, series of wires L1 and Li, M and 22, and 23 and 24, A thermostaticswitch 2i, connected in the wires tit and 24, controls the starting andstopping of the motor in response to predetermined maximum erted andminimum temperatures in the .enclosure to be cooled.

In order to facilitate starting of the compressor I8 when the enclosureto be cooled demands refrigeration and to keep the size of the motor assmall as possible, I have provided means assoeiated with therefrigerating system for reducing the load on the compressor ID byreducing the pressure differential between the high pressure side andlow pressure side of the compressor to a point where easier starting isaccomplished and the absorption of vapor refrigerant by the oil in thecrankcase I8 is minimized.

v In the embodiment of my invention shown in Fig, 1, I- provide aby-passconnection between the discharge side of the compressor i8 andthe suction side or crankcase II, which under certain conditions ofoperation provides a communicatins passage between the high pressure andlow pressure sides of the compressor III. The by-pass connectioncomprises a spring biased and electrically operated valve 25 which isconnected to the discharge conduit ll through a conduit 28 and with thesuction conduit I! through a conduit 28. The valve 25 comprises a bodyportion 38, a top cover portion 3|, and a bottom cover portion 32 all ofwhich are assembled as a unit. A diaphragm 33 is secured in positionbetween the top cover portion 3| and the body portion 38 and serves todivide the space therebetween into a chamber 34 and a chamber 36. Thechamber 34 communicates with the conduit 28 through a conduit 31,thereby subjecting the upper side of the diaphragm 33 to the. pressureof the gas on the discharge side of the system. The chamber 36communicates with the conduit 28 through passages 88 and 4| formed inthe body portion 30, thereby filling the chamber 38 with gas from thelow side of the system and subjecting the lower side of thediaphragm tothe pressure" of the gas in the low side of the system. As shown in Fig.1, a chamber 42 communicating with the passage 38 and opening into achamber 43, at 40, is provided in the body portion 30. The chamber 43 isformed by the bottom cover portion 32 and the body portion 30 andcommunicates with the discharge side of the system through a passage 38.Thus gas from the high side of the system will flow through the openingat 40 into the low side of the system unless some means is provided toclose this opening when such a flow is not desired. I provide for thispurpose a pin valve 44 which is connectedto the diaphragm 33 through apush rod 48 and is held in alignment with the opening 40 by a spring 41,the force of whichvmay be adjusted by a screw 48. Thus the opening andclosing of the pin valve 44 will depend upon the pressure differentialexisting between the high and low sides of the system and the forceexerted by the spring 41 in valve closing direction. In accordance withmy invention, therefore, when using a refrigerant, such asdichlorodifluoromethane, also known as Freon-12, in the refrigeratingsystern, I adjusted the spring 41 to exert a pressure, as for example 40lbs. per sq. in., in a valve closing direction so that when the pressuredifferential between the high and low sides of the system is, forexample, 4 lbs. per sq. in., the forces in valve closing direction willbalance the force in valve opening direction, and when the pressurediflerential is slightly less than the pressure exthe spring 41, thevalve 44 will close and remain closed until the pressure differentialhas been increased to an amount greater than the force exerted by thespring 41. Thus it is apparent that the compressor can be partiallyunloaded and a predetermined pressure differential maintained during the011 cycle of the compressor by simply adjusting the force exerted by thespring 41 to close the valve when the predethe wires 2| 'and 22, andexerts a force which draws an armature 43, which is connected to anextension of the push rod 48, upwardly, thereby closing the opening at40 and shutting off the flow of gas between the high and low sides ofthe system.

Fig. 1.0peration The operation of the refrigerating system embodying thefirst form of my invention is as follows: Assuming that the enclosure tobe cooled demands refrigeration and the switch 21 has closed to energizethe motor l8, refrigerant vapor is compressed in the compressor l0 andis discharged at a high pressure to the condenser l2. The compressedrefrigerantv is cooled and condensed in the condenser l2 and passes as aliquid to the evaporator l3 through a conduit l4 and an expansion valve,shown diagrammatically at It. The refrigerant in the evaporator l3absorbs heat from the enclosure to be cooled and passes as a vapor tothe suction side of the compressor i0.-

As has been explained, hereinbefore, the pin valve is is maintained inthe closed position during the operation of the refrigerating system andthere is no flow of highpressure gas through the bypass connection tothe low side of the system. As is apparent from the drawing, the upperside of the diaphragm 33 is subjected to the pressure of the gas in thehigh side of the system while the under side of the diaphragm 33 issubjected to the pressure in the low side of the system. There is,therefore, a relatively high pressure diiferential between the high andlow sides of the system during the operation of the refri erating systemwhich, except for the force exerted by the solenoid I would overcome theforce exerted by the spring 41 in valve closing direction and cause thepin valve 44 to move out of the opening 40 and permit the flow of gasfrom the high to the low side of the system.

When the temperature of the enclosure to be cooled has reached the lowerlimit for which the thermostat associated with switch 21 is set, themotor l9 will be deenergized and the solenoid 5| will be no longeroperative to maintain the pin valve 44 in the closed position. Thepressure differential existing in the system will be sufficient toovercome the force exerted by the spring 41 and the pin valve 44 willmove down'wardly out of the opening 40 and allow gas to pass from thehigh side to the low side of the system. This flow of gas will continueuntil the pressure differential hasbeen reduced to a predeterminedvalue, for example, slightly'less than 40 lbs. per sq. in., at which theadsorption of refrigerant, such as Freon 12, by the lubricating oil isat a sumciently low value. The upward biasing force of the spring v4'!when. the valve 44 is in the closed position will balance the force invalve-opening direction when the pressure diii'erential is, for

example, 40 lbs. per sq. in. The pin valve will be maintained in theclosed position by the spring 41 when the compressor is stopped and bythe force exerted by the solenoid when the compressor is operating. Thusduring the off cycle of the compressor l0, the load on the compressorhas been sufficiently reduced to place the compressor in immediatecondition for starting while, at the same time, suflicient pressuredifierental between the high and low sides of the system has beenretained to minimize absorption of vapor refrigerant by the lubricatingoil in the crankcase l6.

Fig. 2

. lin the embodiment shown in Fig. 2, partial unloading of thecompressor, when it is shut down, is effected in the same manner as inFig. 1, namely, in response to the pressure differential between thehigh and low sides. This embodiment differs, however, in that closing ofthe valve in the by-pass connection during operation of the compressoris effected by equalizing the pressures on opposite sides. of thepressure-responsive diaphragm 33 in response to pressure developed bythe lubricating oil pump of the compressor. The refrigerating system isthe same as that of Fig. 1.

This embodiment includes a valve 25a which is similar to the valve 25 ofFig. 1 except that the solenoid 5| and the armature 49 are omitted, andthe chamber 36 is not connected to the passage 42, but is connectedthrough a passage 4| and a conduit 53 to a pilot valve 54.

Like reference numerals will therefore be used to designate similarparts in both embodiments and the description of the refrigeratingsystem and the valve 25 already given in connection with Fig. 1 willsuflice for the second embodiment.

The pilot valve 54, which is used to control the operation of the valve25a, comprises a gas chamber 56 and an'oil chamber 51 which are held inspaced relation with each other by brackets 58 and 59. The gas chamber56 is provided with an outlet port 6| opening into the conduit 53 andtwo inlet ports 62 and 63. The inlet port 62 communicates with theconduit 28 through a conduit 64, thereby providing a passage for theflow of gas at discharge pressure into the chamber 56. The inlet port 63communicates with the conduit |1 through a conduit 66 and a passage isthereby provided for gas at suctionpressure into the chcamber 56. Thehigh pressure gas and the low pressure gas in the chamber 56 areseparated from each other by a slide valve 61 which is operated from theoil chamber 51 to set up communication between the outlet port 6| andthe inlet port 62 when the compressor I0 is operating and between theinlet port 63 and the outlet port 6| when the compressor is stopped.Thus when the compressor I0 is operating, both sides of the diaphragn 33are subjected to discharge pressure and when the compressor is 'notoperating, the upper side of the diaphragm 33 is subjected to dischargepressure while the bottom side of the diaphragm is subjected to thepressure of the gas in the low side of the system. The slide valve 61 isconnected to one end of a rod 68 which extends out of the gas chamber 56and into the oil chamber 51 through suitably sealed openings. A piston69 in the oil chamber is attached to the other end of the rod 66 so thatany movement of the piston 69 will produce a like movement of the slidevalve 61. A spring 1| disposed in the oil chamber 51 is arranged tooppose the upward movement of the piston 69, when the piston is actuatedby oil pressure developed by the oil pump 52 and supplied to the oilchamber 51 through a conduit".

Fig, 2.,- -Operation When the compressor I6 is operating, oil pressuredeveloped by the pump 52 will actuate the piston 66 and will cause theslide valve 61 to move upwardly to place the outlet port 6| incommunication with the inlet port 62. Gas from the high side of thesystem will flow into the chamber 36 to subject the lower side of thediaphragm 33 to discharge pressure. Since the upper side of thediaphragm 33 is also subjected to discharge pressure, the pressuredifierential will be zero and the biasing force of the spring 41 willmaintain the pin valve 44 in closed position in the opening 46. The pinvalve 44 will be maintained in the closed position just as long as thecompressor 40 is operating and oil pressure is developed by the pump 52.

When the compressor l6 stops and oil pressure is no longer developed bythe pump 52, the spring 1| will cause the piston 69 to move downwardly.

The slide valve 61 will move below the outlet port 6| thereby cuttingoff communication between the high pressure side of the system and thechamber 36. The outlet port 6| and the inlet port 63 will be broughtinto communication with each other and gas from the low side of thesystem will flow into the chamber 36 to subject the under side of thediaphragm 33 to suction pressure. The upper side of the diaphragm isstill subjected to discharge pressure with the result that the pressuredifierential is' relatively high and is suflicient to' overcome thebiasing force provided by the spring 41. The pin valve 44 will thereforeopen and compressed refrigerant will flow from the high pressure side tothe low pressure side of the system through the by-pass connection. Thisflow of compressed refrigerant will continue until the pressuredifierential has been reduced to a predetermined value, as for thecompressor I6 is stopped. As long as thepresure differential is lessthan the biasing force of the spring 41, as has already been explained,the pin valve 44 will also remain in the closed position when thecompressor I6 is operating as there is no valve opening force opposingthe biasing force of the spring 41. Thus when the compressor II) isstopped, the starting load on the compressor is reduced and, at the sametime, sufficient pressure differential has been retained in the systemin order that the absorption of refrigerant by the lubricating oil willnot be excessive.

It will be apparent from the foregoing that I have provided means forpartially unloading a compressor by which starting of the compressor isfacilitated, the absorption of refrigerant by the lubricating oil isminimized, and slugging of the compressor valves is substantiallyreduced.

While I have shown myinvention in several forms, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various other changes-and modifications without departing from thespirit thereof, and I desire, therefore, that only such limitationsshall be placed thereupon as are imposed by the prior art or as arespecifically set forth in the appended said compressor, an evaporatorconnected to the lowpressu'resideofsaidcompressor,means for admittingcompressedrefrigerant from thehigh pressuresideofsaidcompressortothelowpressure side thereof during the off-cycle of said compressor and meansresponsive to the pressures on the high and low sides of said compressorfor stopping the flow of compressed refrigerant to the low side of saidcompressor when a predetermined minimum pressure differential existsbetween said high and low side. g

3. In refrigerating apparatus, the combination of an intermittentlyoperated compressor, a condenser connected tothe high pressure side ofsaid compressor, an evaporator connected to the low pressure side ofsaid compressor, a by-pass connection between the high pressure side andthe low pressure side of said compressor, a valve in said by-passconnection, means for opening said valve to admit compressed refrigerantfrom the high pressure side to the low pressure side of said compressorwhen said compressor stops and means for closing said valve when apredetermined minimum pressure differential exists between said highpressure side and said lowpressure side.

4. In refrigerating apparatus, a refrigerant circulating systemincluding an evaporator, a condenser andan intermittently operatedcompressor,'a connection between the high pressure side of saidcompressor and the low pressure side thereof, a valve in saidconnection, means for maintaining said valve closed when said compressoris operating and means operable automatically when said compressor isstopped for opening said valve in response to a pressure differentialbetween the high and low sides of said compressor above a predeterminedvalue and for closing said valve in response to a pressure differentialbelow said predetermined value.

5; In refrigerating apparatus, a refrigerant circulatory systemincluding an evaporator, a condenser and an intermittently operatedcompressor, a connection between the high pressure side of saidcompressor and. the low pressure side thereof, a valve in saidconnection, means for maintaining said valve closed when said compressoris operating, and automatically operable means for opening said valvewhen said compressor stops to reduce the pressure on the high pressureside of said system and for closing said valve when the pressuredifferential between the high pressure and low pressure side of saidsystem has been reduced to a predetermined value.

" 6. In refrigerating apparatus, a refrigerant circulatory systemincluding an evaporator, a condenser and an intermittently operatedcompressor, a connection between the high pressure side of saidcompressor and the low pressure side thereof, a valve in saidconnection, magnetic means for maintaining said valve in closed positionwhen said compressor is operating and pressure responsive means foropening said valve when said compressor stops to admit refrigerant fromthe high pressure side of said compressor to the low pressure sidethereof and for closing said valve when said high pressure has beenreduced and said low pressure increased sufficiently to obtain apredetermined pressure differential the pressure on the high side ofsaid system and to increase the pressure on the low side of said systemand for closing said valve when a predetermined pressure differentialexists between said high pressure side and said low pressure side andtemperature responsive means for effecting the operation of said motorand said magnetic means. I

8. In refrigerating apparatus, a refrigerant circulatory system,including an evaporator, a condenser and an intermittently operatedcompressor, a lubricant pump actuated by said compressor, a by-passconnection between the high pressure side of said compressor and the lowpressure side thereof, a valve in said connection, means responsive tothe pressures on the high and low pressure sides of said compressor foractuating said valve and a pilot valve actuated by oil supplied by saidoil pump for controlling. the operation of said pressure responsivemeans.

9. In refrigerating apparatus, a refrigerant circulating systemincluding an evaporator, a condenser and an intermittently operatedcompressor, a lubricant pump actuated by said compressor, a by-Dassconnection between the high piessure side of said compressor and the lowpressure side thereof, a valve in said connection, pressure responsivemeans for operating said valve, and a pilot valve actuated by oil fromsaid lubricant pump for controiling the operation of said pressureresponsive means, said pressure responsive means being effective tomaintain said first valve in a closed position when said compressor isoperating.

10. In refrigerating apparatus, a refrigerant circulating systemincluding an evaporator, a condenser and an intermittently operatedcompressor, an oil pump actuated by said compressor, a by-passconnection between the high pressure side of said compressor and the lowpressure side thereof, a valve in said by-pass connection, pres-Lureresponsive means for operating said valve and a pilot valve responsiveto the oil pressure produced by said oil pump for controlling theoperation of said pressure responsive means, said pressure responsivemeans being effective when said compressor is operating to maintain saidfirst valve in a closed position and when said compressor stops to opensaid first valve to admit compressed refrigerant to the low pressureside of said system and to close said first valve when the pressuredifferential between the high side of said compressor and the lowpressure side thereof has reached a predetermined value.

11. In refrigerating apparatus, a refrigerant circulating systemincluding an evaporator, a condenser and a compressor, a motor fordriving said compressor, an oil pump actuated by said compressor, aby-pass connection between the high pressure side of saidcompressor andthe low pressure side thereof, a valve'in said by-pass connection, aspring for biasing said valve in' valve-closing direction, apressure-responsive element subjected, when the compressor is stopped,in valve-opening direction to the pressure of the gas'on the high sideof the system and in valve-closing direction to the pressure of thegasin the low side of the system and of, a valve in said by-passconnection, pressure responsive means for opening and closing saidvalve, said pressure responsive means including a diaphragm, one side ofwhich is subjected to the pressure on the high pressure side of 'saidpressure developed by said pump for controlling compressor, and a pilotvalve responsive to oil the operation of said pressure responsive means,

said pilot valve being effective when said compressor is operating tosubject the other side of said diaphragm to the pressure on the highpressure side of said compressor to maintain said valve in a closedposition, and when said compressor is notloperating to subject the otherside of said diaphragm to the pressure on the low 7 pressure side ofsaid compressor to, open said valve, said pressure responsive elementclosing said valve in response to a predetermined low,

pressure difierential when said compressor is stopped. a

13. In refrigerating apparatus, a refrigerant circulatory systemincluding a condenser, an evaporator and a compressor, a motor. fordriving said compressor, a by-pass connection between the high and lowpressure side of said compressor, a valve in said by-pass connection,

means for automatically maintaining said valve in closed position whensaid compressor is operating and means responsive to the pressure on thelow side of said system for opening and closing said valve when saidcompressor is not operating.

EDWARD R. WOLFERT.

